CO2, Global Warming and Coral Reefs: Prospects for the Future

One of the long-recognized potential consequences of the ongoing rise in the air’s CO2 content is CO2-induced global warming, which has been predicted to pose a number of problems for both natural and managed ecosystems in the years ahead. Of newer concern, in this regard, are the effects that the ongoing rise in the air’s CO2 content may have on coral reefs. It has been suggested, for example, that CO2-induced global warming will do great damage to corals by magnifying the intensity, frequency, and duration of a number of environmental stresses to which they are exposed. The predicted consequences of such phenomena include ever more cases of coral disease, bleaching, and death.

Increases in the atmosphere’s CO2 content have also been postulated to possess the potential to harm coral reefs directly. By inducing changes in ocean water chemistry that can lead to reductions in the calcium carbonate saturation state of seawater, it has been predicted that elevated levels of atmospheric CO2 may reduce rates of coral calcification, possibly leading to slower-growing – and, therefore, weaker – coral skeletons, and in some cases, death.

Because of these many concerns, and the logical desire of individuals and governments to do something about what they perceive to be bona fide threats to the well-being of the biosphere, it is important to have a correct understanding of the scientific basis for the potential problems that have been predicted. Hence, in the following pages we review the scientific literature on CO2, global warming and coral reefs, in an effort to determine if the ongoing rise in the air’s CO2 content does indeed pose a threat to these incomparable underwater ecosystems. The key findings of this review are as follows:

Ø There is no simple linkage between high temperatures and coral bleaching.

Ø As living entities, corals are not only acted upon by the various elements of their environment, they also react or respond to them. And when changes in environmental factors pose a challenge to their continued existence, they sometimes take major defensive or adaptive actions to insure their survival.

Ø A particularly ingenious way by which almost any adaptive response to any type of environmental stress may be enhanced in the face of the occurrence of that stress would be to replace the zooxanthellae expelled by the coral host during a stress-induced bleaching episode by one or more varieties of zooxanthellae that are more tolerant of the stress that caused the bleaching.

Ø The persistence of coral reefs through geologic time – when temperatures were as much as 10-15°C warmer than at present, and atmospheric CO2 concentrations were 2 to 7 times higher than they are currently – provides substantive evidence that these marine entities can successfully adapt to a dramatically changing global environment. Thus, the recent die-off of many corals cannot be due solely, or even mostly, to global warming or the modest rise in atmospheric CO2 concentration over the course of the Industrial Revolution.

Ø The 18- to 59-cm warming-induced sea level rise that is predicted for the coming century by the IPCC – which could be greatly exaggerated if predictions of CO2-induced global warming are wrong – falls well within the range (2 to 6 mm per year) of typical coral vertical extension rates, which exhibited a modal value of 7 to 8 mm per year during the Holocene and can be more than double that value in certain branching corals. Rising sea levels should therefore present no difficulties for coral reefs. In fact, rising sea levels may actually have a positive effect on reefs, permitting increased coral growth in areas that have already reached the upward limit imposed by current sea levels.

Ø The rising CO2 content of the atmosphere may induce changes in ocean chemistry (pH) that could slightly reduce coral calcification rates; but potential positive effects of hydrospheric CO2 enrichment may more than compensate for this modest negative phenomenon.

Ø Theoretical predictions indicate that coral calcification rates should decline as a result of increasing atmospheric CO2 concentrations by as much as 40% by 2100. However, real-world observations indicate that elevated CO2 and elevated temperatures are having just the opposite effect.

In light of the above observations, and in conjunction with all of the material presented in this review, it is clear that climate-alarmist claims of impending marine species extinctions due to increases in both temperature and atmospheric CO2 concentration are not only not supported by real-world evidence, they are actually refuted by it.